Sheet Metal Construction Truss and its Method of Continuous Automated Manufacture

ABSTRACT

A linear construction truss comprising a hollow shell with a square cross section and a core composed of linked tetrahedra, and a method of manufacturing of said linear construction truss.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Provisional Patent ApplicationNo. 61/460,163, filed Dec. 27, 2010, the contents of which is herebyincorporated by reference.

BACKGROUND

1. Field of Invention

This invention relates to an improved design for a linear constructiontruss and a method of manufacturing said linear construction truss.

2. Prior Art

There are many designs for linear members (beams and trusses) used inconstruction. Such linear members have to be resistant to shear stressand bending, since the loads on them are typically perpendicular to theaxis of the linear member. The I-beam is one example of such a linearmember. While the I-beam is an efficient design in that it concentratesthe material where the largest linear stress is bound to occur, themanufacturing process for making I-beams involves hot rolling, which isvery energy-intensive and environmentally damaging; furthermore, steelI-beams are relatively heavy.

Another possible type of design for a linear member is a hollow sheetmetal box beam, such as the one described in U.S. Pat. No. 2,007,898 toRagsdale. Ragsdale discloses a hollow sheet metal beam with a generallyrectangular cross section. While such beams are lightweight and do notrequire energy-intensive hot rolling methods to construct, a beam with ahollow cross-section is not very strong, and susceptible to buckling.

Due to the advantages offered by a sheet metal construction over anI-beam or a lumber beam, many attempts have been made to reinforce ahollow sheet metal beam from the inside. One such design for areinforced hollow sheet metal beam is disclosed in U.S. Pat. No.3,783,498 to Moyer (shown in FIG. 1). Moyer discloses a beam with ahexagonal cross-section, made of sheet metal and welded. The beam isreinforced at two of its vertical sides with sheet metal strips weldedto those two sides. These strips provide extra strength on the sidesthat bear the most stress. However, due to the fact that the horizontalsides are not reinforced and that there is no reinforcing elements onthe interior of the beam, the resulting linear member is still notstrong enough for some purposes.

Another method of reinforcing the interior of a hollow sheet metal beamis disclosed in U.S. Pat. No. 4,023,683 to Varga. Varga disclosesreinforcing the interior of a hollow sheet metal beam with one or moreplanar webs. While that design is stronger than a simple hollow sheetmetal beam, it is still not strong enough for some constructionapplications. One of the reasons for its relative lack of strength isthat the planar webs are aligned with the axis of the beam, whichincreases the strain on these webs in normal operation.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a linear member (alinear construction truss) that is stronger than prior art reinforcedhollow beams, and to provide a method of manufacturing the linearconstruction truss that does not involve hot-rolled processes.

A linear member designed in accordance with the present invention is alinear construction truss comprising a hollow shell with a squarecross-section and a reinforcing core of linked regular tetrahedra whoseedge length is approximately equal to the inner diagonal of thecross-section of the hollow shell, the core being rigidly attached tothe hollow shell. Such a design offers many advantages, one of thembeing that rather than providing a single planar web to reinforce ahollow beam, the design provides many planar webs (i.e. the faces of thetetrahedra), which are disposed at varying oblique angles relative tothe axis of the linear construction truss. This reduces the linearstrain on the reinforcing material and renders the linear memberstronger. Furthermore, the inter-tetrahedral webs reinforce alternatediagonals of the hollow shell, which also improves its strength andresistance to buckling.

The intra-tetrahedral edges, when joined to the shell, comprise twosingle layer struts, three double layer struts, and two triple layerstruts per linear tetrahedral module. The double and triple layer strutsjoin to form two double layer and two triple layer helices coiling inopposite directions along the length of the truss. These mutuallyreinforcing structures arrange in an X-form triangulation of thediametric shell corners per tetrahedral module, normal to therectangular shell's axis. These bi-directional coiling elements impart acable-like resilience to the structure, and render it stronger thanprior art reinforced hollow beams.

In a preferred embodiment, both the hollow shell and the reinforcingcore are made of sheet metal, though other materials may also be used.Due to its square cross-section, such a linear construction truss can beused in place of a lumber beam or an I-beam in constructionapplications. Furthermore, a sheet metal linear construction truss inaccordance with the present invention is more lightweight than either alumber beam or a steel I-beam and requires only cold-rolled processes tomanufacture. Thus, it offers the advantages of a sheet metal design,while also offering improved strength over prior art reinforced sheetmetal designs.

In a preferred embodiment, the intra-tetrahedral edges that attach tothe hollow shell are chamfered to facilitate attachment to the hollowshell. The inter-tetrahedral edges are not chamfered.

Another aspect of the present invention is a method of continuousautomated manufacture of a linear construction truss as described above.Both the reinforcing core and the hollow shell can be manufactured fromsheet metal strips using simple folding and stamping processes.

In accordance with the manufacturing method of the present invention,two identical sheet metal strips are cut and bent in such a way as toresult in a plurality of triangular faces with specified angles betweenthe triangular faces. In a preferred embodiment of the invention, thereare chamfers between the triangular faces. The two strips are thenintertwined together to form a reinforcing core comprising a pluralityof linked regular tetrahedra, and rigidly attached. A sheet metal shellwith a square cross-section is then formed around the reinforcing coreand rigidly attached to it.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art design of a reinforced hollow sheet metal beam.

FIG. 2 shows a linear construction truss of the present invention.

FIG. 3 shows a separate view of the hollow shell and a separate view ofthe reinforcing core.

FIG. 4 shows a view of one of the two sheet metal strips used to formthe reinforcing core.

FIG. 5 shows a view of one of the two sheet metal strips used to formthe reinforcing core after it is folded in accordance with the presentinvention.

FIG. 6 shows a view of a chamfer between two of the triangular faces ofthe folded sheet metal strip.

FIG. 7 shows a view of the reinforcing core.

FIG. 8 shows two possible designs for a die used to bend the sheet metalstrips that comprise the reinforcing core.

FIG. 9 shows an embodiment of a die forming station.

FIG. 10 shows a view of an embodiment of a core assembly station.

FIG. 11 shows a side view of a web welder module of another embodimentof a core assembly station.

FIG. 12 shows a side view of a chamfer welder module of the sameembodiment of a core assembly station.

FIG. 13 shows an embodiment of a shell application station.

FIG. 14 shows an alternate embodiment of a shell application station.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2 and 3 show the main component parts of the linear constructiontruss of the present invention—the reinforcing core 10 and the shell 20.FIG. 2 is a view of the assembled linear construction truss with atransparent view of the hollow shell. FIG. 3 shows a separate view ofthe reinforcing core and a separate view of the hollow shell. As can beseen in FIG. 2, the reinforcing core 10 comprises a plurality of linkedregular tetrahedra, situated inside a hollow shell 20 with a squarecross-section such that the linked edges of the tetrahedra areapproximately equal to the inner diagonal of the hollow shell. Eachtetrahedron, except for the ones located on each end of the truss, is,rigidly linked to its two neighboring tetrahedra along two of its edges,and rigidly linked to the inner surface of the hollow shell along itsfour other edges. This strengthens the structure by providing numerousplanar reinforcing surfaces at oblique angles to the load. In apreferred embodiment, both the hollow shell and the reinforcing core aredie-formed from continuous sheet metal strips by automated cutting andfolding machines that process rolls of sheet metal; it is preferable,though not required, that the sheet metal strips that form thereinforcing core be thinner than the sheet metal strips that form thehollow shell.

FIG. 4 shows one of the two identical sheet metal strips 30 used to formthe reinforcing core. In a preferred embodiment, the strip is die-cutwith cutouts 100 to facilitate folding and chamfering, and cut withperforations 50 to reduce its weight.

FIG. 5 shows a view of sheet metal strip 30 after it is folded. Thestrip 30 is folded in such a way that the dihedral angles betweensuccessive triangular faces alternate between 109.4667 degrees and289.4667 degrees throughout the length of the strip. For example, thedihedral angle between triangular face 70 and triangular face 71 is109.4667 degrees; the dihedral angle between triangular face 71 andtriangular face 72 is 289.4667 degrees; the dihedral angle betweentriangular face 72 and triangular face 73 is 109.4667 degrees; and soon. This results in a helical shape that can then be intertwined withanother identical shape to form a plurality of linked tetrahedra.

In the preferred embodiment, there are chamfers between the triangularfaces, as shown in FIG. 6, which is a magnified view of a section ofsheet metal strip 30. The bending angles at the edges labeled “A” areapproximately 144.7333 degrees; the bending angles at the edges labeled“B” are approximately 234.7333 degrees. This pattern repeats throughoutthe length of the strip. The chamfers are intended to facilitatewelding, both for welding the two strips together to form the tetrahedraand for welding the tetrahedra to the hollow shell.

FIG. 7 shows the two sheet metal strips 30 and 40 joined together toform the reinforcing core 10. Sheet metal strip 30 is shaded while sheetmetal strip 40 is left unshaded. As can be seen in the figure, eachtetrahedral unit derives its parts from both of the two core strips.From each strip, each tetrahedral unit derives two of its fourtriangular faces, two of its four chamfered edges, and one of its twointer-tetrahedral web layers. The successive inter-tetrahedral weblayers are at right angles to each other and normal to the core axis.The core is thus composed of the two helices of equilateral trianglesand strips that will be precisely coiled together and, in a preferredembodiment, joined with spot or linear welds.

The hollow shell 20 encloses, triangulates, and is welded to, the core10, as is shown in FIG. 2. It is a linear tube with a squarecross-section. Depending on the machinery deployed, it can comprise one,two, or four separate sheet metal strips. These are die-cut and foldedfor corners and edge joining, then welded at the seam or seams andwelded to the core.

The linear construction truss may be manufactured by using cold-rolledprocesses such as stamping or bending. FIG. 8 shows two possible designsfor a die used to form the folded sheet metal strips that comprise thereinforcing core. Die 110 can achieve the folding of two facets per diestrike; die 120 can achieve the folding of four facets per die strike.Alternate numbers of facets may also be used. The chamfer angles areidentified on the drawing. For die 110, the dihedral angle between faces1 and 2 is 109.4666 degrees; the chamfer angles are 144.7333 degrees onthe edges marked A and 234.7333 degrees on the edges marked B. For die120, the dihedral angle between faces 1 and 2 is 109.4666 degrees, as isthe dihedral angle between faces 3 and 4. The dihedral angle betweenfaces 2 and 3 is 289.4667 degrees. The chamfer angles are 144.7333degrees on the edges marked A and 234.7333 degrees on the edges markedB.

FIG. 9 shows one possible embodiment of a die forming station thatcontinuously forms a folded sheet metal strip used to form thetetrahedral reinforcing core. A sheet metal strip 240 is continuouslyfed from a roll 200 into a rotary die cutter 210, which cuts it withcutouts to facilitate folding and chamfering and perforations to reduceits weight. After it is cut, the strip is folded in a die 220. Thefolded strip 250 is then ready to be welded together with a secondidentical strip to form the tetrahedral core.

FIG. 10 shows an overview of one possible embodiment of a core assemblystation that assembles the two folded strips into a tetrahedralreinforcing core. Two folded strips 310 and 320 are continuously fedinto a rotating assembly fixture 330, which rotates around the axis ofthe reinforcing core. The rotating assembly fixture 330 holds the twostrips 310 and 320 in correct angular position for welding by means ofregistration chute 340. Registration chute 340 is an axially revolvingrectangular chute that moves the core forward in steps to the nextoperation. The entire assembly moves forward in steps through therevolving fixture; at each stopping point, automatic welding, performedby a robot 350 or a weld array 360, joins the various weld points of thecore, starting with the inter-tetrahedral web and following with thetetrahedral chamfer-flanges. The reinforcing core is then ready to beassembled with the hollow shell at the shell application station.

Another embodiment of a core assembly station is detailed in FIGS. 11and 12, and comprises two independent modules. One module—the web weldermodule—welds the intertetrahedral webs of the core, and moves the coreforward in steps to the next operation. The other module—the chamferwelder module—welds the chamfered edges of the tetrahedra.

FIG. 11 shows a side view of the web welder module. Truss core 305enters the assembly module from the right side of the drawing, and isheld in the registration chute 315. The main linear actuator 325 movesthe weld frame 327, which contains the vertical and horizontal weldarrays into position for the welding of the intertetrahedral webs. Weldarray 335 is vertical and is used to weld the vertical intertetrahedralwebs; weld array 345 is horizontal and is used to weld the horizontalintertetrahedral webs. Vertical linear actuators 337 move the horizontalweld arrays 345 into position for welding; horizontal linear actuators347 move the vertical weld arrays 335 into position for welding. Themain linear actuator 325 then moves the weld arrays in the directionparallel to the truss core axis and enables them to move the truss corethrough the module; the range of its displacement is labeled as“Dual-Tetra Module Horizontal Displacement” in FIG. 11. Two positions ofthe weld arrays—“A position” and “B position”—are shown in FIG. 11.

FIG. 12 shows a side view of the chamfer welder module. This modulewelds the intratetrahedral edges after the intertetrahedral webs havebeen welded. Truss core 305 enters this module from the right side ofthe drawing, and is held in the registration chute 315. The verticaldiagonal weld arrays 365 are used to weld the intratetrahedral edgesthat are vertical; a corresponding set of horizontal diagonal weldarrays 375 are used to weld the intratetrahedral edges that arehorizontal. Vertical linear actuators 385 and horizontal linearactuators (not shown) bring the weld arrays into position.

One embodiment of the shell application station is shown in FIG. 13. Thefinished core 400 rotates around its axis due to the action of the coreassembly station shown in FIGS. 10-12. Four rolls of sheet metal, 415,425, 435, and 445, rotate along with the core. Rotary dies 455, 465,475, and 485 apply the four strips of sheet metal to the sides of thecore to form the shell; spot weld arrays then weld the strips of sheetmetal to the core and corner welders weld the strips of sheet metaltogether. For clarity, FIG. 13 shows only one spot weld array 495 andone corner welder 497, out of the four required spot weld arrays andfour corner welders. This embodiment is not the preferred embodiment ofthe shell application station because it necessitates that the entireapparatus revolve around the shell axis, which is complex and expensive.

The preferred embodiment of the shell application station is shown inFIG. 14. The finished core 400 is fed into the shell applicationstation; a roll of sheet metal 410 is fed into a diagonal corner folddie 420 and is applied to the core 400 at an angle that enables it to bewrapped around the core 400 in a spiral pattern. This method of applyingthe shell is more efficient because the whole apparatus can remainstationary and only the core 400 rotates. A seam welder 430 welds thesuccessive coils of the spiral together; a spot weld array 440 welds thecore assembly to the shell. A cut-off saw 450 cuts off finished lengthsof the linear construction truss in modular lengths at the tetrahedralweb.

1. A linear construction truss, comprising: a hollow shell with a squarecross-section; a core located inside the hollow shell, comprising aplurality of tetrahedra rigidly connected together at their edges, theedge length of each tetrahedron being approximately equal to the insidediagonal of the cross-section of the hollow shell.
 2. The linearconstruction truss of claim 1, where the core is rigidly connected tothe hollow shell.
 3. The linear construction truss of claim 1, where thetetrahedra are hollow.
 4. The linear construction truss of claim 1,where the tetrahedra are chamfered in such a way that the chamferedsurfaces can be rigidly connected to the sides of the hollow shell. 5.The linear construction truss of claim 3, where at least one face of atleast one tetrahedron has at least one perforation.
 6. The linearconstruction truss of claim 1, where the hollow shell and the core aremade of sheet metal.
 7. A method of manufacturing a linear constructiontruss, comprising: bending a first sheet metal strip in such a way as toresult in a plurality of equilateral triangular faces where the altitudeof each triangular face approximately equals the width of the sheetmetal strip, such that: the angle between a first triangular face and asecond triangular face is approximately 109.4667 degrees; the anglebetween the second triangular face and a third triangular face isapproximately 289.4667 degrees; the angle between the third triangularface and a fourth triangular face is approximately 109.4667 degrees; theangles between neighboring faces continue to alternate betweenapproximately 109.4667 degrees and approximately 289.4667 degreesthroughout the length of the first sheet metal strip; bending a secondsheet metal strip identically to the first sheet metal strip; rigidlyconnecting the first sheet metal strip and the second sheet metal stripin such a way as to result in a core of linked tetrahedra; forming ahollow shell with a square cross-section such that the length of theinner diagonal of the cross-section is approximately equal to the edgelength of the tetrahedra; rigidly connecting the core to the hollowshell.
 8. The method of claim 7, where the bending step compriseschamfering the area between the triangular faces in such a way that thechamfer surfaces can be rigidly connected to one of the sides of thehollow shell.
 9. The method of claim 7, where the forming step compriseswinding a strip of sheet metal around the core in a spiral pattern inorder to form the hollow shell.
 10. The method of claim 7, where theforming step comprises winding a plurality of strips of sheet metalaround the core in a spiral pattern in order to form the hollow shell.11. The method of claim 7, where the forming step comprises rigidlyconnecting four sheet metal sides on the outside of the tetrahedral corein order to form the sides of the hollow shell.
 12. The method of claim7, where prior to the bending step, one or both of the first sheet metalstrip and the second sheet metal strip are cut in such a way that theperforations do not impinge on the edges of the tetrahedra.